1. Field of the Invention
This invention relates to a semiconductor device and, more particularly, to a semiconductor device which comprises a substrate having a die-bonding area and being formed with a plurality of wire-bonding pads outside the die-bonding area, die-bonding a semiconductor chip onto the die-bonding area, and connecting the semiconductor chip to the wire-bonding pads by bonding wires.
2. Description of the Prior Art
A conventional semiconductor device 1 of this kind shown in FIG. 11 includes a substrate 2 formed of an insulative material such as a polyimide, glass epoxy or ceramic and etc. The substrate 2 is formed with a wiring pattern 3 of a copper (Cu) foil on the surface. An insulating film (resist) 4 is applied so as to cover the wiring pattern 3. It is noted, as shown in FIG. 12, the wiring pattern 3 includes electrodes 3a and wire-bonding pads (hereinafter referred to as xe2x80x9cWB padxe2x80x9d) 3b. The resist 4 is applied so as not to cover the WB pads 3b. Returning to FIG. 11, a semiconductor chip (hereinafter referred merely to as xe2x80x9cchipxe2x80x9d) 5 is on the resist 4 and die-bonded, by a die-bonding member 6, onto a die-bonding area 2a of the substrate 2 shown in FIG. 12. It is noted in FIG. 12, the substrate 2 (die-bonding area 2a) and the wiring pattern 3 are shown partially (approximate one quarter). As shown in FIG. 11, electrical connection is made, by metal thin wires (bonding wire) 7 such as a gold wire, between electrode pads 5a provided on the chip 5 and the WB pads 3b included in the wiring pattern 3. Furthermore, the chip 5 and the bonding wires 7 are sealed by a mold resin (mold) 8 such as an epoxy resin. Then, bumps 9 as an external connecting electrode are joined to the electrodes 3a included in the wiring pattern 3 through through-holes 2a formed on the substrate 2 from a rear surface of the substrate 2. In this manner, a CSP (Chip Size Package) or BGA (Ball Grid Array) type semiconductor device has been formed.
In such a prior art, in the case of a chip 5 having a little smaller size than the die-bonding area 2a is bonded, the bonding wires 7 can be bonded onto the WB pads 3b as shown in FIG. 12. However, as shown in FIG. 13, in the case a chip 5 having a smaller size than the chip shown in FIG. 12 and the same shape is bonded, there occurs a problem that the bonding wire 7 is brought into contact with the adjacent WB pads 3b at the K portion. That is, as shown in FIG. 14, since each bonding wire 7 is provided with a smooth curved potion 7a in the vicinity contacting each WB pad 3b to absorb stress applied during bonding, the curved portion 7a is brought into contact with adjacent WB pads 3b when the bonding wire 7 traverses the adjacent WB pads 3b. That is, it causes a short-circuit.
Although forming the wiring pattern 3 according to the size of a chip would be appropriate to avoid this, there is a problem that it takes time to develop the wiring patterns 3, and thus a mounting up cost is increased.
Therefore, it is a primary object of the present invention to provide a semiconductor device capable of shortening development time period and reducing design cost.
It is another object of this invention to provide a semiconductor device capable of preventing occurrence of defective mount caused by ball fall.
A semiconductor device according to this invention comprising: a substrate having a die-bonding area and formed with a plurality of wire-bonding pads outside the die-bonding area; a semiconductor chip die-bonded onto the die-bonding area; and bonding wires connecting the semiconductor chip to the wire-bonding pads, wherein the wire-bonding pads are so formed that the lengthwise directions thereof are in parallel or approximately in parallel to lines extending from a center of the die-bonding area to bonding positions of the wire-bonding pads.
A semiconductor device according to this invention includes the substrate having flexibility such as a polyimide. The substrate has on its surface the area (die-bonding are) to die-bond the semiconductor chip (chip) thereonto. The wire-bonding pad (WB pad) to wire-bond the bonding wires is provided in plural outside the die-bonding (DB) area on the substrate. The WB pads are so formed that the lengthwise directions thereof are in parallel or approximately in parallel to the lines extending from the center of the DB area to bonding positions, i.e. radiative lines. Accordingly, if a chip having a size (the first size) little smaller than the DB area is die-bonded, the bonding wires are approximately in parallel to the lengthwise directions of the WB pads. Even if a chip having a smaller size (the second size) than the first size but the same shape is die-bonded, the bonding wires are also in parallel to the lengthwise directions of the WB pads. That is, even if chips are different in sizes, the same or similar shape permits the bonding wires to be in parallel to the lengthwise directions of the WB pads. Accordingly, a substrate (film carrier) formed with one kind of a wiring pattern can be used regardless of the size of a chip. That is, it is possible to use a film carrier commonly.
According to this invention, since a common film carrier can be used regardless of the change of the size of a chip, there is no need to develop wiring patterns for each size of chip. That is, development of only one wiring pattern can shorten development time period of a wiring pattern. Furthermore, design cost can be reduced.
In one aspect of this invention, a plurality of through-holes are formed on the substrate, and electrodes are formed at the die-bonding area on the substrate in correspondence to the through-holes. Solder balls are electrically connected (joined) to the electrodes through the through-holes. At this time, on the assumption that a diameter of each solder ball is A and a diameter of each through-holes is B, if the relation between A and B is made A/B less than 1.25, the force that made the solder ball in a spherical shape is never larger than the joint force between the solder ball and the electrode. Accordingly, when mounting such the semiconductor device on a printed circuit board, ball fall (phenomenon to cause the solder ball to be separated from the electrode) almost never occurs. Due to this, incidence of defective mount can be significantly reduced.
A semiconductor device according to another invention comprising: a substrate formed with through-holes; a plurality of electrodes formed inside a die-bonding area on the substrate and coupled to a plurality of wire-bonding pads formed outside the die-bonding area; and a plurality of solder balls formed on a rear surface of said substrate and connected to the electrodes through the through-holes, wherein A/B less than 1.25 is satisfied on assumption that a diameter of each solder ball is A and a diameter of each through-hole is B.
A semiconductor device according to another invention has the area (die-bonding area) to die-bond the chip on the substrate having flexibility such as a polyimide. The plurality of wire-bonding pads (WB pad) connected to the semiconductor chip by bonding wires are provided outside the die-bonding (DB) area. Meanwhile, the substrate has the through-holes through which the solder balls are connected to the plurality of electrodes provided from the rear surface of the substrate to the DB area and coupled to the WB pads. On the assumption that a diameter of each solder ball is A, a diameter of each through-hole is B and the relation A/B less than 1.25 is satisfied, the force acting on the solder ball to make it in a spherical shape is never larger than the joint force between the solder ball and the electrode. The relation of A/B less than 1.25 is obtained from experiments by the inventors as a condition to prevent ball fall.
According to another invention, ball fall can be prevented, significantly reducing incidence of defective mount.
In another aspect of this invention, the WB pads are so formed that the lengthwise directions thereof are in parallel or approximately in parallel to the lines extending from the center of the DB area to bonding positions, i.e. radiative lines. Accordingly, in the case a chip having a size (the first size) little smaller than the DB area is bonded, the bonding wires are approximately in parallel to the lengthwise directions of the WB pad. Even if a chip having a smaller size (the second size) than the first size but the same shape is bonded, the bonding wires are in parallel to the lengthwise directions of the WB pads. That is, even if chips are different in sizes, the same or similar shape permits the bonding wires to be in parallel to the lengthwise directions of the WB pads. Accordingly, a substrate (film carrier) formed with one kind of the wiring pattern can be used regardless of the size of a chip. That is, a film carrier can be used commonly.
The above described objects and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.